Method for acquiring image and ion beam apparatus

ABSTRACT

A method for acquiring an image, in which an image of an image acquiring region is acquired by radiating an ion beam to a sample having a conducting part with a linear edge on a dielectric substrate, includes performing an equal-width scan of the ion beam in a first direction that obliquely intersects the linear edge and sweep in a second direction intersecting the first direction. The ion beam is sequentially scanned in different patterns on different scan regions of parallelogram shape, each of which includes the image acquiring region. Secondary charged particles are detected to generate image data of all the scan regions, and image data of the scan regions are calculated to generate image data of the image acquiring region. The image data of the image acquiring region are synthesized to display the image data of the image acquiring region.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of Japanese Patent Application No.2015-192660, filed on Sep. 30, 2015, which is hereby incorporated byreference in its entirety into this application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to a method for acquiring animage, and an ion beam apparatus.

2. Description of the Related Art

A process of scanning and sweeping an ion beam across a target (asample), in which a conductor is present on an insulator, to observe orprocess the sample is used for many applications. For example, there isrepair of a mask used to produce a semiconductor device and so on.

The mask has a mask pattern of a conductive material such as a metal ona transparent dielectric substrate such as a glass. The mask screenslight in a shape of the mask pattern. The mask pattern has an isolatedpattern or the like in which striped lines and spaces arrangedvertically and horizontally, or small rectangles are present. In thisway, the shape of the mask pattern mostly has pattern edges in alldirections. The repair of the mask does not remake a front surface ofthe expensive mask when there are defects or the like in a pattern ofthe mask, but repairs only the defects or the like, which isadvantageous from an economical and temporal standpoint.

In the repair of the mask, an ion beam is scanned and swept across thepattern edge of the mask in a horizontal or orthogonal direction.

As a similar technology, for example, an X-ray mask examination devicefor scanning and sweeping across an X-ray mask to acquire or examine(observe) an image is described in Patent Literature 1. It is alsodescribed in the X-ray mask examination device that an electron beam isscanned across a pattern edge of a line shape in an orthogonal directionor is scanned and swept across a rectangular mask pattern in a parallelor orthogonal direction.

PRIOR ART LITERATURE Patent Literature

(Patent Literature 1) Japanese Unexamined Patent Application PublicationNo. S63-307728

SUMMARY OF THE INVENTION

However, the conventional image acquiring method and the conventionalion beam apparatus have problems as follows.

When the sample in which the conducting part is present on the insulatoris observed or processed by the ion beam, sometimes a shape or a size ofthe image acquired by the ion beam cannot be accurately determined. Inthis case, one factor is that the insulating part on scan and sweepregions of the ion beam is charged by scan and sweep. Since the wider anarea of the insulating part surrounding the conducting part to beobserved, the more an amount of electrification, and since the scannedand swept ion beam is influenced by charged electric charges, theconducting part approximates a minute conducting part such as a defect,and thus a deformed image is acquired, or no image is acquired.

FIGS. 14A and 14B are top views illustrating an example of a sample inwhich a conducting part is present on an insulator and a scan directionof an ion beam in a related art. In FIG. 14A, within an observationfield of view, a plurality of metal line patterns (conductors) 130Yextending in a shown longitudinal direction are formed on a glass panel131 acting as an insulator at an interval in a shown transversedirection. An exposure part of the glass panel 131 extends between theside-by-side metal line patterns 130Y in the longitudinal direction. Anisolated metal pattern (a conductor) 132 having a smaller contour thanline widths of the metal line patterns 130Y exists between theneighboring metal line patterns 130Y. For example, the isolated metalpattern 132 may be a normal pattern, a defect of the mask, or the like.In any case, to examine or repair the pattern, images corresponding tocontours of the metal line patterns 130Y and the isolated metal pattern132 need to be accurately acquired.

FIG. 14B illustrates a state of an observation field of view of anotherregion. FIG. 14B is different from FIG. 14A only in that the patternsextend in a shown longitudinal direction. That is, within theobservation field of view, two metal line patterns 130X extending in atransverse direction are formed, and an isolated metal pattern 132 isformed on a glass panel 131 between the metal line patterns 130X.

To acquire an image of each observation field of view, scan and sweep ofan ion beam are performed. A scan direction of the ion beam is atransverse direction (see a shown thin arrow) directed from the shownleft side toward the shown right side. A sweep direction of the ion beamis a longitudinal direction directed from the shown upper side towardthe shown lower side.

In the case of a field of view range of FIG. 14A, the ion beam scannedover the isolated metal pattern 132 is scanned in a directionperpendicular to the extending direction of the metal line patterns130Y. For this reason, the ion beam is radiated to the insulating partonly by a length corresponding to transverse distances A1 and A2 betweenthe isolated metal pattern 132 and the metal line patterns 130Y on theglass panel 131.

In the case of a field of view range of FIG. 14B, the ion beam scannedover the isolated metal pattern 132 is scanned in the extendingdirection of the metal line patterns 130X. For this reason, the ion beamis radiated to the insulating part only by a length corresponding totransverse distances B1 and B2 between the isolated metal pattern 132and left and right ends of the field of view range on the glass panel131.

In the two figures, since the length by which the ion beam is radiatedto the insulating part has a relationship of (A1+A2)<(B1+B2), the amountof electrification of the glass panel 131 is more in FIG. 14B. For thisreason, in the example of FIG. 14A, an image of the isolated metalpattern 132 can be clearly acquired, whereas, in the example of FIG.14B, the image of the isolated metal pattern 132 is deformed ordislocated. When the amount of electrification is considerable, or whenthe isolated metal pattern 132 is small, sometimes the image of theisolated metal pattern 132 cannot be acquired at all.

In this way, when the ion beam is scanned and swept across the regionwhere the conductive isolated pattern is present on the insulating part,there is a great difference between the isolated patterns that can beacquired by an expanding direction of the insulating part surroundingthe isolated pattern and the scan direction of the ion beam. If presenceor a shape of the isolated pattern cannot be accurately recognized, thiscauses a problem that interferes with examination or processing based onthe ion beam apparatus.

Accordingly, the present invention has been made keeping in mind theabove problems, and an object of the present invention is to provide amethod for acquiring an image and an ion beam apparatus that is capableof easily acquiring an image in which an influence of charges on adielectric substrate is reduced when an image of the dielectricsubstrate in which a conducting part having a linear edge is formed isacquired using an ion beam.

In order to accomplish the above object, a method for acquiring an imageof a first aspect of the present invention acquires an image of an imageacquiring region by radiating an ion beam to a sample having conductingparts with linear edges on a dielectric substrate, and includes: a firstoperation of performing an equal-width scan caused by the ion beam in afirst direction that obliquely intersects the edges and sweep in asecond direction intersecting the first direction, and radiating the ionbeam to a scan region of a parallelogram shape wider than the imageacquiring region; a second operation of detecting secondary chargedparticles generated by radiating the ion beam to generate image data ofthe scan region; a third operation of calculating the image data of thescan region to generate image data of the image acquiring region; and afourth operation of displaying the image data of the image acquiringregion.

In the method for acquiring the image, the first operation may beperformed a plurality of times by changing at least one of a scandirection of the equal-width scan and a sweep direction of the sweep andsetting output of the ion beam such that a total amount of irradiationof the ion beam in the image acquiring region becomes an amount ofirradiation required when an image is acquired by one sweep; the secondoperation may be performed after the first operation is performed eachof the plurality of times; and the third operation may synthesize aplurality of image data that are generated by the second operationperformed a plurality of times and are based on the image data in thescan region, and thereby generates the image data of the image acquiringregion.

The method for acquiring the image may further include: before theplurality of image data based on the image data in the scan region aresynthesized in the third operation, a fifth operation of detecting anamount of position offset between the image data in the scan region thatis generated by the second operation performed at least the first of theplurality of times in which the second operation is performed and theimage data in the scan region that is generated by the second operationperformed the final times; and a sixth operation of correcting aplurality of amounts of position offset of the image data in the scanregion on the basis of the amount of position offset detected by thefifth operation.

An ion beam apparatus of a second aspect of the present inventionincludes: an ion beam column configured to generate an ion beam used toacquire an image of an image acquiring region of a dielectric substrateon which conducting parts with linear edges are formed and radiate theion beam to the dielectric substrate; a movable stage configured tosupport the dielectric substrate to be movable within at least a planeintersecting an optical axis of the ion beam column; an ion beamirradiation control device configured to control the ion beam column toperform an equal-width scan caused by the ion beam in a first directionthat obliquely intersects the edges and sweep in a second directionintersecting the first direction and radiate the ion beam to a scanregion of a parallelogram shape wider than the image acquiring region; adetector configured to detect secondary charged particles generated fromthe dielectric substrate when the ion beam is radiated; an image datagenerator configured to generate image data of the scan region on thebasis of detected output of the detector; a storage configured to storethe image data of the scan region; a calculator configured to calculatethe image data of the scan region to generate image data of the imageacquiring region; and a display unit configured to display the imagedata of the image acquiring region.

In the ion beam apparatus, the ion beam irradiation control device maycause the ion beam column to radiate the ion beam a plurality of timesby changing at least one of a scan direction of the equal-width scan anda sweep direction of the sweep and setting output of the ion beam suchthat a total amount of irradiation of the ion beam on the imageacquiring region becomes an amount of irradiation required when an imageis acquired by one sweep; and the calculator may synthesize a pluralityof image data that are generated by the image data generator wheneverthe ion beam is radiated a plurality of times and are based on the imagedata in the scan region, and thereby generates the image data of theimage acquiring region.

In the ion beam apparatus, the calculator may be configured to: detectan amount of position offset between the image data in the scan regionthat is generated at least first among the plurality of image data inthe scan region and the image data in the scan region which is generatedfinally; and correct a plurality of amounts of position offset of theimage data in the scan region on the basis of the amount of positionoffset.

According to the method for acquiring the image and the ion beamapparatus of the present invention, there is exerted an effect that,when the image of the dielectric substrate on which the conducting partswith the linear edges are formed is acquired using the ion beam, theimage reducing the influence of the electrification of the dielectricsubstrate can be easily acquired.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic system configuration view illustrating an exampleof a configuration of an ion beam apparatus of a first embodiment of thepresent invention;

FIG. 2 is a block diagram illustrating primary function components of acontrol device of the ion beam apparatus of the first embodiment of thepresent invention;

FIG. 3 is a schematic view illustrating an example of an image acquiringregion and a scan region based on the ion beam apparatus of the firstembodiment of the present invention;

FIG. 4 is a flow chart illustrating a flow of a method for acquiring animage of the first embodiment of the present invention;

FIG. 5 is a schematic top view illustrating an example of a substrate,an image of which is acquired by the ion beam apparatus of the firstembodiment of the present invention;

FIGS. 6A to 6C are schematic views illustrating an example of a scanpattern in the method for acquiring the image of the first embodiment ofthe present invention;

FIGS. 7A to 7D are schematic views illustrating an example of a scanpattern in the method for acquiring the image of the first embodiment ofthe present invention;

FIG. 8 is a schematic view illustrating an overlapping method of thescan pattern in the method for acquiring the image of the firstembodiment of the present invention;

FIGS. 9A and 9B are schematic views illustrating scan and sweep effectsin the method for acquiring the image of the first embodiment of thepresent invention;

FIG. 10 is a schematic view illustrating an example of a position-offsetimage;

FIG. 11 is a schematic view illustrating an example of a scan pattern ofa comparative example;

FIG. 12 is a schematic view illustrating an example of a scan pattern ina method for acquiring an image of a modification (a first modification)of the first embodiment of the present invention;

FIG. 13 is a schematic system configuration view illustrating an exampleof a configuration of an ion beam apparatus of a second embodiment ofthe present invention;

FIGS. 14A and 14B are top views illustrating an example of a sample inwhich a conducting part is present on an insulator and a scan directionof an ion beam in a related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In all the drawings,even in the case of different embodiments, the same or equivalentmembers will be given the same symbols, and common description thereofwill be omitted.

First Embodiment

A method for acquiring an image and an ion beam apparatus of a firstembodiment of the present invention will be described.

FIG. 1 is a schematic system configuration view illustrating an exampleof a configuration of an ion beam apparatus of a first embodiment of thepresent invention.

An ion beam apparatus 10 of the present embodiment illustrated in FIG. 1radiates an ion beam to a sample having a metal pattern on a substrateformed of an insulating material such as a glass panel, and performsprocessing of the metal pattern. An example of the processing performedby the ion beam apparatus 10 may include, for instance, repair of aphotomask used in fabricating a semiconductor device, and so on. The ionbeam apparatus 10 repairs a defect of a mask using, for instance,sputtering etching, gas-assisted etching, or gas-assisted deposition. Toperform this repair, the ion beam apparatus 10 can acquire an image of asurface of a sample according to the method for acquiring the image ofthe present embodiment.

The ion beam apparatus 10 can detect a defect of the metal pattern fromthe acquired image, and perform the repair on the defect.

The ion beam apparatus 10 is provided with a sample chamber 13, a samplestage (a movable stage) 15, an ion beam column 11, a detector 18, anetching gas feeder 16, a deposition gas feeder 17, a monitor (a displayunit) 19, and a control device 20.

The sample chamber 13 has a mask (a sample) 14 that is housed thereinand is repaired by the ion beam apparatus 10. A vacuum exhaust device(not shown) is connected to the sample chamber 13, so that a degree ofvacuum inside the sample chamber 13 can be changed.

The sample stage 15 movably maintaining the mask 14 is disposed in thesample chamber 13. The ion beam column 11 radiating an ion beam towardthe sample stage 15 is disposed in the sample chamber 13 at a positionfacing the sample stage 15. In the present embodiment, the ion beamcolumn 11 is disposed such that an optical axis 12 of an ion beam opticsis parallel to a vertical axis.

The sample stage 15 has a loading surface within a plane intersecting adirection in which the ion beam is radiated from the ion beam column 11.The mask 14 is placed on the loading surface of the sample stage 15. Thesample stage 15 supports the placed mask 14 to be movable at leastwithin the plane intersecting the direction in which the ion beam isradiated.

In the ion beam apparatus 10 illustrated in FIG. 1, as an example, thesample stage 15 can independently move along two axes (hereinafterreferred to as X and Y axes) that are orthogonal to each other in ahorizontal plane.

A direction orthogonal to the X and Y axes is defined as a Z axis. Inthe present embodiment, the Z axis of the sample stage 15 is coaxialwith the optical axis of the ion beam optics. However, for the purposeof easy viewing, the Z axis of FIG. 1 is depicted at a positiondeviating from the optical axis.

The sample stage 15 may have a degree of movement freedom in addition totranslation motions following the X and Y axes.

In the present embodiment, the sample stage 15 is made up of a 5-axismovement mechanism configured of a combination of an XYZ-axial stage, atilt state, and a rotary stage, which are not shown. The XYZ-axial stagetranslates each axis direction of the aforementioned X, Y, and Z axes.The tilt stage obliquely moves around the aforementioned X or Y axis.The rotary stage rotates about the above Z axis.

In the present embodiment, the sample stage 15 is communicatablyconnected with the control device 20 to be described below. The samplestage 15 is operated by an operation instruction that is input from anoperator through an input unit (not shown) or the monitor 19. Further,the sample stage 15 may be operated according to an operationinstruction that the control device 20 (to be described below) generatesas needed.

The ion beam column 11 generates the ion beam, and radiates the ion beamtoward the mask 14 on the sample stage 15.

In the present embodiment, the ion beam apparatus 10 performs the repairof the mask.

The ion beam column 11 is provided with an ion source that generatesions, a lens that focuses the ions generated from the ion source, adeflector that scans and sweeps the ion beam over a sample surface, aniris that passes a part of the ion beam, and so on. However,illustration of their known internal structures are omitted in FIG. 1.

A type of the ion source is not limited as long as the ion source canfocus the ions on a minute diameter to form the ion beam. The ion sourcepreferably has high focusability of the ion beam because an image, inwhich the higher the focusability of the ion beam, the more excellentthe image resolution, is obtained.

An example of the ion source that can be adequately used for the ionbeam column 11 may include, for instance, a gas field ion source, aliquid metal ion source, a plasma ion source, and so on.

The deflector deflects the ion beam within a plane orthogonal to theoptical axis of the ion beam optics focusing the ions. For this reason,the deflector can scan and also sweep the ion beam within a scan plane(a plane intersecting an optical axis of the lens) in an arbitrarydirection.

The ion beam column 11 is communicatably connected with the controldevice 20 to be described below. An ion beam current value, a scandirection or velocity of the ion beam, and a sweep direction or velocityof the ion beam are set for the ion beam column 11 on the basis of acontrol signal from the control device 20. The ion beam column 11performs a scan and sweep operation according to these setting values.

The detector 18 detects secondary charged particles generated when theion beam from the ion beam column 11 is radiated to the sample. In thepresent embodiment, the secondary charged particles detected by thedetector 18 are at least one of secondary ions and secondary electrons.

The detector 18 is obliquely disposed above the sample stage 15 in thesample chamber 13. The detector 18 is communicatably connected with thecontrol device 20 to be described below. The detector 18 transmits thedetected output to the control device 20.

When selective removal repair of the conducting part such as the metalpattern on the mask 14 is performed, the etching gas feeder 16accelerates etching caused by the irradiation of the ion beam, and feedsa gas (an etching gas) that selectively removes a specific place on thesample.

An example of the etching gas may include, for instance, a halogen-basedgas such as iodine.

The etching gas feeder 16 is communicatably connected with the controldevice 20 to be described below. The etching gas feeder 16 feeds theetching gas on the basis of the control signal from the control device20.

When the metal pattern on the mask 14 is formed or is repaired torecover a loss thereof, the deposition gas feeder 17 feeds a gas (adeposition gas) that forms a deposition film at a specific position onthe sample by radiating the ion beam. An example of the deposition gasmay include, for instance, a carbon-based gas, a silane-based gas, and acarbon-based compound gas containing a metal such as tungsten.

A film formed of, for instance, carbon, silicon oxide, platinum, ortungsten can be formed on the mask 14 by radiating an ion beam ofnitrogen or the like while spraying the deposition gas from thedeposition gas feeder 17 at a repair place on the mask 14. As a result,the mask in which a defect does not transfer the defect despiteexposure, can normally transfer a pattern.

The monitor 19 is communicatably connected with the control device 20 tobe described below. The monitor 19 displays an image based on imageinformation transmitted from the control device 20.

An image based on image data of an image acquiring region of the mask 14that is obtained from the detected output of the detector 18 by themethod for acquiring the image of the present embodiment to be describedbelow is included in the image information transmitted from the controldevice 20.

Example of other images that the monitor 19 displays may include ascreen (an operation input screen) that inputs operation conditions foroperating constituent portions of the ion beam apparatus 10 such as theion beam column 11, the sample stage 15, and so on, and a screen thatshows an operation state of the ion beam apparatus 10.

The control device 20 controls an operation of each constituent portionof the ion beam apparatus 10.

The control device 20 at least performs control of a repair operation ofthe mask 14 (hereinafter referred to simply as repair operation) and acontrol of an image acquiring operation of the mask 14 (hereinafterreferred to simply as image acquiring operation) based on the ion beam.

For example, the control device 20 controls operations of the ion beamcolumn 11 and the etching gas feeder 16, thereby performing removalrepair using the ion beam. As a result, in comparison with the case inwhich the etching gas is not introduced, high-speed processing of themask pattern is possible, or only a desired material can be selectivelyremoved.

For example, the control device 20 controls operations of the ion beamcolumn 11 and the deposition gas feeder 17 to perform deposition repairusing the ion beam.

The ion beam is radiated while spraying an organic metal gas ofplatinum, tungsten, or the like from the deposition gas feeder 17 overthe mask 14, thereby elements of the gas component can be deposited. Forexample, the ion beam is radiated while spraying a carbon gas of pylene,naphthalene, phenanthrene, or the like, or a silane-based gas oftetramethylcyclotetrasiloxanes (TMCTS) or the like from the depositiongas feeder 17 over the defect part of the metal pattern, thereby cutparts can be recovered with a carbon film or a silicon oxide layer.

In any case of the repair operation and the image acquiring operation,the control device 20 performs display control of the monitor 19. Thecontrol device 20 displays the operation input screen on the monitor 19,and receives operation input of an operator into the ion beam apparatus10 through the operation input screen.

The control device 20 controls the operations of the ion beam column 11,the detector 18, and the monitor 19, thereby performing the imageacquiring operation. The image acquiring operation is based on themethod for acquiring the image of the present embodiment to be describedbelow.

Hereinafter, primary function components of the control device 20related to the image acquiring operation will be described in brief withreference to FIG. 2.

Details associated with an operation of each function component will bedescribed in the overall operations of the ion beam apparatus 10 to bedescribed below.

FIG. 2 is a block diagram illustrating the primary function componentsof the control device of the ion beam apparatus of the first embodimentof the present invention.

As illustrated in FIG. 2, the control device 20 is provided with an ionbeam irradiation control device 21, an image data generator 23, astorage 24, a calculator 25, and a display control device 26.

The ion beam irradiation control device 21 controls an ion beamradiating operation of the ion beam column 11, synchronizes with the ionbeam radiating operation, and controls operations of the respectiveconstituent portions within the ion beam apparatus 10.

For this reason, the ion beam irradiation control device 21 iscommunicatably connected to the ion beam column 11, the image datagenerator 23, and the calculator 25.

In the image acquiring operation, the ion beam irradiation controldevice 21 sets a scan region of the ion beam.

FIG. 3 is a schematic view illustrating an example of an image acquiringregion and a scan region based on the ion beam apparatus of the firstembodiment of the present invention.

As illustrated in FIG. 3, an image acquiring region P is a rectangularregion displayed on the monitor 19 in the mask 14. The image acquiringregion P is of a rectangle having points Pa, Pb, Pc, and Pd as vertexes.The points Pa, Pb, Pc, and Pd are disposed in this order in a shownclockwise direction. Hereinafter, an axis parallel to a side between thepoints Pa and Pb (or a side between the points Pd and Pc) is defined asan x axis, and an axis parallel to a side between the points Pd and Pa(or a side between the points Pc and Pb) is defined as a y axis.

The x and y axes correspond to deflecting directions of the two axes ofthe ion beam column 11.

A scan region SA1 of the ion beam is of a parallelogram having pointsSa1, Pb, Sc1, and Pd with vertexes. The point Sa1 is a point adjacent tothe point Pa on a linear extension line passing through the points Pdand Pa. The point Sc1 is a point adjacent to the point Pc on a linearextension line passing through the points Pb and Pc.

An intersecting angle at which a side between the Pd and Sc1 (or a sidebetween the points Sa1 and Pb) is made with the y axis is +θ (where)0°<θ<90°) when measured from the y axis. Here, a sign of theintersecting angle is the positive sign in a shown counterclockwisedirection and the negative sign in a shown clockwise direction.

The image acquiring region P may be of a square or a rectangle. When theimage acquiring region P is of the square, the intersecting angle θ isset to, for instance, 45°.

When the image acquiring region P is of the rectangle, a contour of thescan region SA1 may be of a rhombus that is a type of parallelogram.

As indicated by a shown arrow, the scan direction of the ion beam on thescan region SA1 is a direction directed the point Sa1 toward the Pb. Forthis reason, each scan line of the ion beam obliquely intersects the xand y axes.

Since each scan line is parallel to the side between the points Sa1 andPb, lengths (scan widths) of the scan lines are identical to each other.

The sweep direction of the ion beam on the scan region SA1 is adirection following the y axis. For example, the sweep direction may bea direction directed from the point Sa1 toward the point Pd or in theopposite direction.

A scan pattern in which the inside of the aforementioned scan region SA1is scanned directed from the point Sa1 toward the point Pb is defined asa scan pattern Sp1.

As will be described below, in the present embodiment, the ion beamirradiation control device 21 further sets three scan regions inaddition to the scan region SA1. The scan direction of the ion beam isreversed on each scan region, and thereby seven types of scan patterns(to be described below) are obtained in addition to the scan patternSp1.

The ion beam irradiation control device 21 controls the scan and thesweep operation of the ion beam on the basis of eight types of scanpatterns.

The ion beam irradiation control device 21 controls the ion beam currentvalue determining output of the ion beam in each scan pattern. In thepresent embodiment, the ion beam current value can be set to a propervalue through the operation screen of the ion beam apparatus 10 on thebasis of an amount of irradiation (a dose) of the ions that an operatorproperly sets according to a type of the mask 14 or the like. The ionbeam current value can be properly set according to a type of the scanpattern or the number of scan patterns.

An ion beam current of each scan pattern is set as follows. Throughexperience, an operator can determine the amount D of irradiation (adose or the number of ions per unit area) of the ion beam for obtaininga good image on a region that is not originally influenced by charging.When D is equally set to each of the plurality of scan patterns, theamount of irradiation of the ion beam is excessive on the scan and sweepregion. For this reason, an ion beam current capacity and the number ofsweeps are set such that an amount d of irradiation of the ion beam foreach scan pattern has a value given by dividing D by the number N (whereN=8) of scan patterns.

In the present embodiment, settable scan patterns and current values Iaccording to a type of the mask 14 are previously stored in the ion beamirradiation control device 21.

In the present embodiment, the number N of scan patterns used as adefault is 8.

The ion beam irradiation control device 21 controls the deflector suchthat the ion beam is scanned from a start point toward an end point ineach scan pattern, and blanks the scan of the ion beam when one scanline reaches the end point. The blanking refers to perform deflectioncontrol such that the ion beam does not reach the sample for a time fromthe end of the scan of one scan line to the start of the scan of thenext scan line.

After the blanking, the ion beam irradiation control device 21 scans theion beam with the scan width that is parallel and identical to a firstscan line from a new start point that is slightly displaced from aposition of a first start point in a sweep direction. The ion beamirradiation control device 21 repeats this control, thereby performingthe scan and sweep operation of the ion beam on the entirety of oneregion.

The ion beam irradiation control device 21 notifies the image datagenerator 23 (to be described below) of a timing of the start of thescan of the first scan line and a timing of the end of the scan of thelast scan line in each scan pattern.

When the scan and the sweep are completed in all the scan patterns foracquiring the image of the image acquiring region P, the ion beamirradiation control device 21 notifies the calculator 25 (to bedescribed below) that all of the scans and the sweeps are completed.

The image data generator 23 is communicatably connected to the detector18, the ion beam irradiation control device 21 (to be described below),and the storage 24.

The image data generator 23 receives detected output from the detector18. Timings of the start and end of the scan of one scan pattern arenotified to the image data generator 23 from the ion beam irradiationcontrol device 21. The image data generator 23 generates image data onthe basis of the detected output from the start to the end of the scanof one scan pattern. For this reason, the image data generator 23generates image data (hereinafter referred to as scan region image data)on each of the scan regions in each of the plurality of scan patterns.

The image data generator 23 stores each of the generated scan regionimage data in the storage 24.

The calculator 25 is communicatably connected to the ion beamirradiation control device 21, the storage 24, and the display controldevice 26.

When it is notified from the ion beam irradiation control device 21 thatall of the scans and the sweeps are completed, the calculator 25 beginsto generate the image data of the image acquiring region P.

The calculator 25 analyzes a series of scan region image data associatedwith one image acquiring region P stored in the storage 24, and detectsan amount of position offset between the scan region image data. Ifnecessary, the calculator 25 corrects the amount of position offset inthe scan region image data.

The calculator 25 synthesizes each of the scan region image data afterthe amount of position offset is corrected as needed, and extracts theimage data (referred to as image acquiring region image data) on theimage acquiring region P from the synthesized scan region image data.

The calculator 25 transmits the extracted image acquiring region imagedata to the display control device 26.

In the image acquiring operation, the display control device 26 displaysthe image acquiring region image data transmitted from the calculator 25on the monitor 19.

A device configured of the control device 20 is a computer made up of acentral processing unit (CPU), a memory, an input/output interface, anexternal memory, etc., and thus a proper control program for generatinga control signal as described above is executed.

Next, an operation of the ion beam apparatus 10 will be describedcentered on an operation relevant to the method for acquiring the imageof the present embodiment.

FIG. 4 is a flow chart illustrating a flow of the method for acquiringthe image of the first embodiment of the present invention.

Steps S1 to S4 shown in FIG. 4 are performed to acquire the image of themask 14 by the ion beam apparatus 10.

Step S1 is a step including an operation of disposing the mask 14 actingas the sample at an observing position.

An operator disposes the mask 14 on the sample stage 15. The operatorperforms operation input from the monitor 19 to position the mask 14with respect to the ion beam column 11.

Here, an example in which the mask 14 is arranged will be described.

FIG. 5 is a schematic top view illustrating an example of a substrate,an image of which is acquired by the ion beam apparatus of the firstembodiment of the present invention. However, FIG. 5 illustrates a stateof a surface within the image acquiring region P out of the surface ofthe mask 14.

As illustrated in FIG. 5, various mask patterns are formed on thesurface of the mask 14 according to use of the mask 14.

As illustrated in FIG. 5, a line-and-space pattern is formed at a partof the mask 14 by a plurality of metal line patterns (conductionpatterns or conducting parts) 30 that are parallel to each other on aglass panel (an insulating part or a dielectric substrate) 31. The metalline patterns 30 are the conducting parts, and a region interposedbetween the metal line patterns 30 is an insulating part (a space) towhich the glass panel 31 is exposed.

Edges 30 a, each of which extends along a boundary with the insulatingpart in a linear shape, are formed at opposite ends of each of the metalline pattern 30 in a line width direction.

An isolated pattern (a conduction pattern or a conducting part) 32separated from each of the metal line patterns 30 is formed on theinsulating part. The isolated pattern 32 is a normal pattern or a defectformed without intention.

When an image including the metal line patterns 30 as illustrated inFIG. 5 is acquired, the mask 14 is disposed such that the edges 30 a areparallel to the x or y axis of the image acquiring region P. In FIG. 5,as an example, the edges 30 a are disposed to be parallel to the y axis.

In a certain case, the metal line patterns 30 are bent on another regionin view of pattern design at an angle of 90° or 45°. In this case, abent region and a bent direction are known in advance. An extendingdirection of each of the metal line patterns 30 has a previously knownpositional relationship with respect to the contour of the mask 14 or analignment mark formed within the mask 14.

First, an operator fits the contour or the alignment mark of the mask 14in a proper direction with respect to an array reference on the XY planeof the sample stage 15, and places the mask 14 on the sample stage 15.Then, the operator adjusts the sample stage 15 by rotation about the Zaxis to be matched with the x or y axis of a previously known deflectingdirection of the ion beam.

Afterwards, the operator drives the sample stage 15 to perform Z-axialpositioning such that the surface of the mask 14 is located at apreviously known focal plane of the ion beam column 11 or fitting afocus of the ion beam to the surface of the mask.

Then, the operator displaces the sample stage 15 within the XY plane,and displaces a region for observing the mask 14 directly below anobserving position of the ion beam.

In this way, the mask 14 is located at the observing position asillustrated in FIG. 5.

Since the metal line patterns 30, each of which has a rectangular shapewith right-angled portions, mainly occupy a mask used to fabricate asemiconductor, when some of the metal line patterns 30 are positioned tobe parallel to the y axis, the other metal line patterns extending in adirection perpendicular to the positioned metal line patterns arepositioned to be parallel to the x axis.

Unless specifically mentioned, the following description will made withan example in which an image within the image acquiring region Pillustrated in FIG. 5 is acquired.

When step S1 is completed, step S2 is performed as illustrated in FIG.4.

This step is a step including an operation of changing the scan patternto acquire a plurality of image data on each scan region.

Prior to describing a detailed operation of this step, the scan patternused in the present embodiment will be described.

FIGS. 6A, 6B, and 6C, and FIGS. 7A, 7B, 7C, and 7D are schematic viewsillustrating an example of the scan pattern in the method for acquiringthe image of the first embodiment of the present invention.

A scan pattern Sp2 illustrated in FIG. 6A is different from the scanpattern Sp1 (see FIG. 3) only in that the scan direction of the ion beamis reversed. In the scan pattern Sp2, a scan direction is a directiondirected from a point Pb toward a point Sa1.

A scan pattern Sp3 illustrated in FIG. 6B is a scan pattern equivalentto reversing the scan pattern Sp1 to shown left and right (in an x-axialdirection).

A scan region SA2 of the scan pattern Sp3 is a parallelogram havingpoints Pa, Sb2, Pc, and Sd2 as vertexes. The point Sb2 is a pointadjacent to the point Pb on a linear extension line passing through thepoints Pc and Pb. The point Sd2 is a point adjacent to the point Pd on alinear extension line passing through the points Pa and Pd.

An intersecting angle at which a side between the points Pa and Sb2 (ora side between the points Sd2 and Pc) is made with the y axis is −θ whenmeasured from the y axis.

The scan direction of the ion beam is a direction directed from thepoint Sb2 to the point Pd, as depicted by a shown arrow.

A scan pattern Sp4 illustrated in FIG. 6C is different from the scanpattern Sp3 only in that the scan direction of the ion beam is reversed.

The scan pattern Sp4 is a scan pattern equivalent to reversing the scanpattern Sp2 to be shown left and right (in an x-axial direction).

A scan pattern Sp5 illustrated in FIG. 7A is a scan pattern equivalentto the scan pattern Sp4 that is rotated 90° in a counterclockwisedirection.

A scan region SA3 of the scan pattern Sp5 is a parallelogram havingpoints Sa3, Pb, Sc3, and Pd as vertexes. The point Sa3 is a pointadjacent to the point Pa on a linear extension line passing through thepoints Pa and Pb. The point Sc3 is a point adjacent to the point Pc on alinear extension line passing through the points Pd and Pc.

An intersecting angle at which a side between the points Sa3 and Pd (ora side between the points Pb and Sc3) is made with the y axis is +θ whenmeasured from the y axis.

The scan direction of the ion beam is a direction directed from thepoint Pd to the point Sa3, as depicted by a shown arrow.

A scan pattern Sp6 illustrated in FIG. 7B is different from the scanpattern Sp5 only in that the scan direction of the ion beam is reversed.

A scan pattern Sp7 illustrated in FIG. 7C is a scan pattern equivalentto the scan pattern Sp6 that is reversed to be shown from top and bottom(in a y-axial direction).

A scan region SA4 of the scan pattern Sp7 is a parallelogram havingpoints Pa, Sb4, Pc, and Sd4 as vertexes. The point Sd4 is a pointadjacent to the point Pd on a linear extension line passing through thepoints Pc and Pd. The point Sb4 is a point adjacent to the point Pb on alinear extension line passing through the points Pa and Pb.

An intersecting angle at which a side between the points Sa3 and Pd (ora side between the points Pb and Sc3) is made with the y axis is −θ whenmeasured from the y axis.

The scan direction of the ion beam is a direction directed from thepoint Sd4 to the point Pa, as depicted by a shown arrow.

A scan pattern Sp8 illustrated in FIG. 7D is different from the scanpattern Sp7 only in that the scan direction of the ion beam is reversed.

Here, an overlapping method of each scan pattern will be described.

FIG. 8 is a schematic view illustrating an overlapping method of thescan pattern in the method for acquiring the image of the firstembodiment of the present invention.

As illustrated in FIG. 8, all of the scan patterns Sp1 to Sp8 areprovided to cover all the image acquiring region P. To this end, a totalof eight types of scan patterns overlap on the image acquiring region P.Each number given within the figure indicates the number of overlappedscan patterns. Triangular regions (e.g., a triangle having points Pa,Pb, and m1 as vertexes, and so on) on which four types of scan patternsoverlap are formed outside the image acquiring region P in four places,and triangular regions (e.g., a triangle having points Sa1, Pa, and m1as vertexes, and so on) on which two types of scan patterns overlap areformed outside the image acquiring region P in eight places.

In this way, in the present embodiment, the image acquiring region P ismultiply scanned and swept across a maximum of eight types of scanpatterns in multiple directions by the ion beam. However, since theregions other than the image acquiring region P have low scan and sweepoverlap of the ion beam, damage to the sample surface caused by theirradiation of the ion beam is low.

In step S2, the order of scanning and sweeping the scan patterns Sp1 toSp8 is not particularly restricted. Hereinafter, the scan and the sweepare carried out in the order of the scan patterns Sp1 to Sp8 by way ofexample.

This step is initiated when an operator designates the image acquiringregion through the monitor 19 and performs operation input for beginningto acquire an image, and when the control device 20 receives thisoperation input.

In this operation input, the operator may designate a pattern, anintersecting angle at which the ion beam is scanned, a type of the scanpattern, the number of scan patterns, and a current value of the ionbeam.

If there is no designation of the operator, the ion beam irradiationcontrol device 21 of the control device 20 sets the use of the scanpatterns Sp1 to Sp8 as a default. Further, the ion beam irradiationcontrol device 21 automatically sets the current value of the ion beamin each of the scans and the sweeps.

First, the ion beam irradiation control device 21 transmits an operationinstruction based on the scan pattern Sp1 to the ion beam column 11.Simultaneously, the ion beam irradiation control device 21 notifies theimage data generator 23 to initiate the scan and the sweep.

The ion beam column 11 scans and sweeps the ion beam over the mask 14 onthe basis of the scan pattern Sp1.

Here, a first direction that is the scan direction of the ion beam is adirection directed from the point Sa1 toward the point Pb on the scanregion SA1. A second direction that is the sweep direction of the ionbeam is a direction of the y axis. The second direction obliquelyintersects the first direction.

When the ion beam is radiated to the mask 14, secondary chargedparticles, for instance, secondary electrons are emitted from anirradiator.

When the detector 18 detects the secondary charged particles, thedetector 18 transmits detected output to the image data generator 23 inturn.

The image data generator 23 notified to initiate the scan and the sweepbegins to generate image data on the basis of the detected outputtransmitted from the detector 18.

The ion beam is scanned and swept over a target region.

If there is an insulating part on an irradiating region, the insulatingpart is charged. Some of charged electric charges are diffused throughthe neighboring conducting part during blanking, so that the chargedelectric charges are reduced. The longer a blanking time, the smaller anamount of electrification. However, if the blanking time is indefinitelylong, this is not preferable because a time to observe or process adesired region is increased. In contrast, if the blanking time is short,electrification is overlapped by next scan of the ion beam in a state inwhich previous electrification is not reduced, and the amount ofelectrification is increased. Further, when the blanking time is notuniform whenever the ion beam is scanned or when a scanning time of theion beam is different for each scan line, the electrification becomesnon-uniform on an entire image forming region, and a stain occurs at anacquired image. For this reason, it is important to control the ion beamsuch that the scan is performed with the same width by setting a fixedscanning time and a fixed blanking time that are suitable for apredetermined region.

Therefore, when the image acquiring region is a rectangle (or a square),a parallelogram having oblique sides inclined with respect to one sideof the rectangle and two sides adjacent to the one side becomes anoptimum shape.

When the scan and the sweep based on the scan pattern Sp1 are completed,the ion beam irradiation control device 21 notifies the image datagenerator 23 of the completion of the scan and the sweep.

The image data generator 23 notified of the completion of the scan andthe sweep completes generation of the image data. The generated imagedata is image data of a range of the scan region SA1 based on the scanpattern Sp1. Hereinafter, the image data is referred to as scan regionimage data Gs1. The image data generator 23 stores the scan region imagedata Gs1 in the storage 24.

In this way, acquiring the scan region image data Gs1 based on the firstscan and sweep is completed.

After the scan region image data Gs1 is stored, the ion beam irradiationcontrol device 21 performs the same control as the foregoing except thatthe scan pattern Sp2 is replaced with the scan pattern Sp1.

In the present embodiment, when the scan and the sweep based on one scanpattern are completed, and the storage of the scan region image datacaused by the image data generator 23 is completed, the ion beamirradiation control device 21 immediately performs control for next scanand sweep.

When the scan and the sweep based on the scan pattern Sp8 are completedby repeating this operation, scan region image data Gs1 to Gs8 arestored in the storage 24.

When the scan and the sweep of the scan pattern Sp8 are completed, theion beam irradiation control device 21 notifies the calculator 25 thatall of the scans and the sweeps are completed.

Now, step S2 is completed.

After step S1 is carried out, the edges 30 a of each of the metal linepatterns 30 are aligned to be parallel to the y axis.

For this reason, the scan and sweep operation based on each scan patternin step S2 includes a first operation of performing equal-width scan ina first direction that obliquely intersects the edges 30 a and sweep ina second direction that intersects the first direction and of radiatingthe ion beam to a scan region that has a parallelogram shape and iswider than the image acquiring region P.

Further, the sweep of one scan pattern may be performed once or aplurality of times.

Further, the first operation is performed by changing at least one of ascan direction of the equal-width scan and a sweep direction of thesweep and setting a current value of the ion beam and the number ofsweeps such that a total amount of irradiation of the ion beam on theimage acquiring region P becomes an amount of irradiation that is usedfor obtaining an image suitable for a region having nearly the same areaand which an operator or a control device knows in advance.

A second operation is performed at each time after the first operationperformed a plurality of times.

Further, the second operation of generating scan region image data Gs1by detecting secondary charged particles generated by radiating the ionbeam is included in step S2.

Here, before step S3 is described, scan and sweep effects in step S2will be described.

FIGS. 9A and 9B are schematic view illustrating scan and sweep effectsin the method for acquiring the image of the first embodiment of thepresent invention.

Each of the scans and the sweeps in step S2 is performed on the basis ofthe scan patterns Sp1 to Sp8. As in the scan direction depicted in FIG.9A by a solid arrow, in any case, the scan direction is obliquelyintersected at an intersecting angle ±θ with respect to the y axis onthe image acquiring region P. For this reason, the edge 30 a extendingin the y-axial direction that is the first direction is obliquelyintersected at an intersecting angle ±θ.

The ion beam that scans the isolated pattern 32 crosses the edges 30 aof one of the neighboring metal line patterns 30, passes through thesurface of the glass panel 31 that is the insulating part, and reachesthe isolated pattern 32. The ion beam passing through the isolatedpattern 32 comes out of the isolated pattern 32, passes through thesurface of the glass panel 31, crosses the edges 30 a of the other ofthe neighboring metal line patterns 30, and reaches the metal linepattern 30.

The insulating part of the mask 14 is charged when scanned with the ionbeam. The charged electric charges are reduced depending on the blankingtime, but they are left to some extent.

To make it difficult for the ion beam to be influenced by the leftcharged electric charges, it is necessary to reduce as much as possiblea distance at which the ion beam passes through the insulating partbefore and after the ion beam passes through the conducting part.

In the case of FIG. 9A, the distance at which the ion beam passesthrough the insulating part can be minimized in the scan line passingthrough the isolated pattern 32. This is to select the scan directionfollowing the x axis (see an arrow with a shown broken line).

In contrast, as depicted by an arrow with a shown chain double-dashedline, the scan line passing through the isolated pattern 32 in the scandirection following the y axis is scanned over the insulating partexcept that it passes through the isolated pattern 32 acting as theconducting part. When the isolated pattern 32 is a micro pattern, thedistance at which the ion beam passes through the insulating part isnearly equal to a width of the image acquiring region P in the y-axialdirection.

For this reason, the influence of the charged electric charges of theinsulating part is increased, so that an image of the isolated pattern32 is deformed or cannot be checked.

In the embodiment, since an intersecting angle between the edge 30 a andthe scan line is ±45°, the distance at which the ion beam passes throughthe insulating part is about 1.4 times, in comparison with the case inwhich the scan direction is the x-axial direction.

For example, a line interval of the metal line pattern 30 is defined asw, a length of each side of the image acquiring region P is defined as W(where W>w), a size of each side of the isolated pattern 32 is definedas Δ (where Δ<w). Since the distance at which the ion beam passesthrough the insulating part in the scan direction of the shown brokenline is w−Δ, the distance at which the ion beam passes through theinsulating part in each scan direction of the present embodiment becomes1.4×(w−Δ). In contrast, the distance at which the ion beam passesthrough the insulating part in the scan direction of the shown chaindouble-dashed line is W−Δ. For this reason, if 1.4×w<W, the distance atwhich the ion beam passes through the insulating part is sharply reducedin the case of the scan of the present embodiment. The condition can besatisfied by properly setting the size of the image acquiring region Pfor the metal line patterns 30.

In this way, as in the present embodiment, the ion beam is scanned in adirection inclined with respect to the y axis. Thereby, in comparisonwith the case in which the scan direction is the y-axial direction, itis possible to reduce the influence of the charged electric charges.

The scan pattern of the present embodiment is preferable above all whenthe conducting parts extending in the y-axial direction and theconducting parts extending in the x-axial direction are mixed within onemask 14.

FIG. 9B illustrates an example of a case in which, metal line patterns(conduction patterns or conducting parts) 34 extending in the x-axialdirection are present as the image acquiring region P.

In this case, for the same reason as described above, the influence ofthe charged electric charges becomes the maximum when the scan directionis the x-axial direction (see an arrow with a shown broken line). Forexample, if the scan direction is optimized for the metal line patterns30 and is selected in the x-axial direction in FIG. 9A, it is impossibleto acquire a good image on the image acquiring region P as in FIG. 9B.For this reason, there is a need to examine directions of the patternsof the conducting parts on each image acquiring region P, and to changethe scan direction as a result.

However, according to the present embodiment, in any case of FIGS. 9Aand 9B, the influence of the charged electric charges is small, andfurther is admitted to the same extent. For this reason, it is possibleto omit the step of examining the directions of the patterns of theconducting parts in detail to set the scan direction, and easily acquirea good image. As a result, it is possible to reduce a work time requiredfor the observation of the image.

Further, in the present embodiment, an amount of irradiation of the ionbeam in one scan pattern is set to 1/N of an amount D of irradiation ofthe ion beam required when an image is originally acquired by one scanand sweep.

When a current value (or a dose) of the ion beam radiated in this way isreduced, an amount of detection of the secondary charged particles isreduced. Thus, a contrast of the image is reduced to a certain extent.

However, since an amount of electrification in the scan and the sweepbased on one scan pattern is reduced, the influence of the chargedelectric charges on the ion beam in the insulating part is reduced.

That is, each scan region image data becomes image data that more fullyreproduces arrangement of the conducting parts despite a low contrast.

Next to step S2, step S3 is performed. This step is a step including anoperation of synthesizing the image data based on the scan region imagedata Gs1 to Gs8.

This step is initiated by the calculator 25 when it is notified from theion beam irradiation control device 21 that all of the scans and thesweeps are completed.

In this step, the calculator 25 may perform an operation (a fifthoperation) of detecting an amount of position offset, an operation (asixth operation) of correcting the amount of position offset, and anoperation (a third operation) of synthesizing an image in this order.

In the operation of detecting the amount of position offset, thecalculator 25 detects an amount of position offset of the scan regionimage data Gs8 generated by final scan and sweep from the scan regionimage data Gs1 generated by the first scan and sweep that is at leastperformed in step S2.

As described above, in the present embodiment, the charged electriccharges per scan and sweep are small. However, since the scan and thesweep are repeated, the charged electric charges are graduallyaccumulated on the surface of the mask 14. For this reason, depending onan amount of accumulation of the charged electric charges, the ion beamthat scans and sweeps the image acquiring region P has a chance of beingbent on the whole under the influence of the charged electric charges.As a result, a position of the generated scan region image data issometimes drifted (position-offset) within the xy plane. Further, insome cases, the acquired image deviates due to mechanical micromotionsuch as drift of the sample stage.

FIG. 10 is a schematic view illustrating an example of a position-offsetimage.

For example, in an example of the image illustrated in FIG. 10, the scanregion image data Gs8 is parallel displaced relative to the scan regionimage data Gs1 depicted by a chain double-dashed line in a positivedirection of the x axis (to a shown right side) by a distance d on thewhole.

This position offset of the image is one example. An amount of positionoffset (a size and a direction) is different depending on an amount ofelectrification of the mask 14, a mask pattern of the mask 14, an amountof irradiation of the ion beam, or the like.

The calculator 25 detects an amount of relative position offset bycomparison between the scan region image data.

To be specific, in the present embodiment, the amount of position offsetof the image in the xy plane is detected by specifying positions ofcharacteristic portions representing the same spots between the scanregion image data.

The characteristic portion of the scan region image data that is usedfor the detection of the amount of position offset may include an edge,a corner, etc. which can be regarded to have no defects. The scan regionimage data of the present embodiment has high shape reproducibilitybecause the influence of the charged electric charges is low. However,the amount of position offset may be detected by, particularly,extracting a shape of the defect portion.

Further, the amount of position offset of the image may be detected bysome of the characteristic portions of the scan region image data aswell as image matching of the entire image within the image acquiringregion P.

The amount of position offset detected by image comparison between thescan region image data Gs8 caused by the final scan and sweep and thescan region image data Gs1 has a high possibility that magnitude thereofbecomes maximum. Hereinafter, this amount of position offset is referredto as an amount of whole position offset.

The amount of position offset detected by the calculator 25 is notlimited to the amount of overall position offset.

For example, a plurality of amounts of position offset may be detectedby image comparison among the scan region image data Gs8, one of thescan region image data Gs2 to Gs7, and the scan region image data Gs1.

Hereinafter, an amount of position offset caused by the image comparisonbetween one of the scan region image data Gs2 to Gs7 and the scan regionimage data Gs1 is referred to as an amount of partial position offset.

In the present embodiment, the calculator 25 detects only the amount ofwhole position offset as an example. The amount of position offset ofthe edge that can be regarded to be normal as the characteristic portionof the image data is obtained. For example, in the case of FIG. 10, anamount d of movement in the positive direction of the x axis of the edge30 a in the scan region image data Gs1 and Gs8 is detected as the amountof whole position offset.

In the operation of correcting the amount of position offset, ifnecessary, the calculator 25 corrects the amounts of position offset ofthe scan region image data Gs1 to gs8 on the basis of the amount ofpositional offset detected by the operation of detecting the amount ofpositional offset. In the present embodiment, since the amount ofpositional offset of the scan region image data Gs1 that becomes areference of the amount of positional offset is regarded to be 0 (zero),no correction is performed.

In the operation of detecting the amount of positional offset, when onlythe amount of whole position offset is detected, the calculator 25corrects the amount of position offset for each scan region image databy distributing an amount of whole detection as the amount of positionoffset of each scan region image data. A method of the distribution maybe proportionally distributed, or be non-linearly distributed accordingto a change characteristic of the position offset when the changecharacteristic of the position offset is known.

In the operation of detecting the amount of positional offset, when oneor more amounts of partial position offset are detected, the calculator25 calculates the amount of position offset of each scan region imagedata on the basis of interpolation using the amount of whole positionoffset and the amount of partial position offset.

In the present embodiment, the amount d of whole position offset isequally divided, and the amounts of position offset of the scan regionimage data Gs2 to Gs7 are corrected. To be specific, the calculator 25displaces the scan region image data Gsi (where i=1 to 8) in a negativedirection of the x axis by (i−1)d/7. The image data after thedisplacement are shown as scan region image data gs1 to gs8.

The calculator 25 maintains the scan region image data gs1 to gs8 in thestorage 24. Further, in the aforementioned description, attention ispaid to an amount of offset of the scan image region (the imageacquiring region P). However, without being limited thereto, acharacteristic shape (a reference pattern) around the image acquiringregion P may be determined in advance, an image of the reference patternmay be acquired whenever each scan pattern is scanned and swept, and theamount of offset of the image acquiring region may be determined from anamount of offset of the reference pattern.

Now, the operation of detecting the amount of position offset and theoperation of correcting the amount of position offset are completed.

Afterwards, the calculator 25 performs the operation of synthesizing theimage (overlapping and integrating the image).

In the operation of synthesizing the image, the calculator 25synthesizes the scan region image data gs1 to gs8 which the scan regionimage data Gs1 to Gs8 have been corrected. The scan region image datags1 to gs8 are image data based on the respective scan region image dataGs1 to Gs8.

The calculator 25 performs calculation by reading and adding image dataof a range of each image acquiring region P out of the scan region imagedata gs1 to gs8 stored in the storage 24. As a result, the calculator 25generates an image acquiring region image data GP having a size of theimage acquiring region P.

The calculator 25 stores the generated image acquiring region image dataGP in the storage 24.

Now, the operation of synthesizing the image is completed, and step S3is completed.

Since the scan region image data gs1 to gs8 are acquired by radiatingthe ion beam according to an amount D/8 of irradiation of the ion beam,each signal intensity becomes about ⅛, and each SN ratio is low.

However, in the present embodiment, as described above, the deformationof the shape, or the like resulting from the influence of theelectrification of the mask 14 is reduced. For this reason, the scanregion image data gs1 to gs8 are image data more accurate than an imageobtained by performing one scan and sweep with high intensity inrelation to positional information.

Further, in the present embodiment, in that the amount of positionoffset is corrected in the scan region image data gs1 to gs8, the imagedata that are more accurate in relation to the positional informationare added.

These scan region image data are added, and thereby the image acquiringregion image data GP becomes a clear image because the same signalintensity as the image obtained by performing one scan and sweep withhigh intensity is obtained.

Since the synthesized scan region image data gs1 to gs8 are acquiredfrom a plurality of scan directions, when noise caused by the chargedelectric charges is shown, the shown method differs depending on thescan direction. As a result, since there is no addition like correctimage data, the image data becomes low-intensity image data within theimage acquiring region image data GP. For this reason, an SN ratio ofthe image acquiring region image data GP is increased compared to theindividual scan region image data.

As the calculation that the calculator 25 performs on the scan regionimage data, the synthesizing operation based on the addition between thescan region image data has been described by way of example. Thecalculator 25 may perform another calculation of the scan region imagedata before it synthesizes the scan region image data. For example, thecalculator 25 may perform calculations such as image enhancementprocessing, averaging processing, noise removal processing, and so on.

Next to step S3, step S4 is performed. This step is a step including anoperation (a fourth operation) of displaying the image acquiring regionimage data GP.

The calculator 25 transmits the image acquiring region image data GPstored in the storage 24 to the display control device 26. The displaycontrol device 26 displays the image based on the image acquiring regionimage data GP on the monitor 19.

Now, step S4 is completed.

An operator determines whether or not there is a defect within the imageacquiring region P using the image displayed on the monitor 19, and mayinitiate a repair operation as needed.

After step S4 is completed, the operator displaces the mask 14 withinthe XY plane using the sample stage 15, and thereby can acquire an imageat another spot of the mask 14 in the same way as described above.

However, the operator is sometimes aware that, in a size range of theimage acquiring region P of the mask 14, there is no spot where theedges of the conducting part are fitted to the scan direction. In thiscase, the operator may omit step S1, and start from step S2.

For example, the edges of the mask pattern of the mask used to fabricatethe semiconductor extend in directions perpendicular to each other inmost cases. For this reason, for example, in step S1, when thedirections of the edges are fitted to the y axis, the directions of theedges are fitted to the x axis at a spot of another mask patternperpendicular to the y axis, and thus positioning caused by rotationabout the Z axis again is not required.

For this reason, since step S1 does need not to be repeated, rapid imageacquisition can be performed.

As described above, in the present embodiment, the ion beam is scannedin the direction that obliquely intersects the linear edges in the mask14, and is also swept a plurality of times with the scan directionchanged, and the image data obtained by each scan pattern is integrated.For this reason, when the ion beam passes through the isolated pattern32, the scan of the ion beam across the long insulating part can bereduced, so that the influence of the electrification can be reduced. Asa result, a good image is obtained.

That is, the ion beam is scanned in the direction that obliquelyintersects the linear edges. Thereby, even when a scan length of theinsulating part is slightly increased in any scan pattern, the scanlength of the insulating part may be overwhelmingly shortened in anotherscan pattern. Thus, it is possible to obtain the image in which theinfluence of the electrification is greatly reduced by integrating(overlapping) the image obtained by these plurality of scan patterns.

Further, since the amount of irradiation of the ion beam to each scanpattern is small, the image of one scan pattern becomes an image inwhich the influence of the electrification is low and a stain is little.These images are integrated a plurality of times, and thereby a goodquality of image can be acquired.

According to the ion beam apparatus 10 and the method for acquiring theimage of the present embodiment using the same, when the image of thedielectric substrate in which the conducting parts, each of which hasthe linear edges, are formed is acquired using the ion beam, it ispossible to easily acquire the image in which the influence of theelectrification of the dielectric substrate is reduced.

Further, in the present embodiment, since the scan width (the scan time)of the ion beam in each scan pattern are identical to each other withinthe scan patterns, the amount of irradiation of the ion beam for eachscan line is constant. The amount of electrification per scan line ismade constant, and thereby the influence of the charged stain of themark 14 can be suppressed.

This will be described with reference to FIG. 11.

FIG. 11 is a schematic view illustrating an example of a scan pattern ofa comparative example.

A scan pattern Spr of a comparative example illustrated in FIG. 11 is ascan pattern that has the same scan and sweep directions as the scanpattern Sp1 and scans only the inside of an image acquiring region P.

In this scan and sweep method, a scan width (a scan time) of the ionbeam differs according to a place. To be specific, a scan width of ascan line passing through points Pb and Pd is longest, and the scanwidth is more shortened as the scan line passes through a region closerto points Pa and Pc.

When the scan and the sweep are performed on the basis of this scanpattern Spr, a blanking time differs according to the scan line, andthus an amount of electrification differs according to the place. Forthis reason, a difference (a stain) in brightness of the image occursaround the points Pa and Pc and the points Pb and Pd of the imageacquiring region. According to distribution of the amount ofelectrification, the image may be deformed.

In contrast, in the scan pattern of the present embodiment, sinceequal-width scan is performed, the blanking time is constant. An imagehaving uniform image brightness according to a sweep place is obtained.

First Modification

Next, a method for acquiring an image and an ion beam apparatus of amodification (a first modification) of the present embodiment will bedescribed.

This modification is an example in which the scan pattern is changed inthe first embodiment, and is different only in the scan pattern storedin the ion beam irradiation control device 21. Hereinafter, themodification will be described centered on differences from the firstembodiment.

FIG. 12 is a schematic view illustrating an example of a scan pattern ina method for acquiring an image of a modification (a first modification)of the first embodiment of the present invention.

As illustrated in FIG. 12, a scan pattern Sp11 of this modification isscanned and swept on a rectangular scan region SB1 circumscribed aroundan image acquiring region P.

The scan region SB1 is a rectangle having points Sm1, Sm2, Sm3, and Sm4as vertexes. A side between the points Sm4 and Sm1 is a segment thatpasses through a point Pa and is inclined from a y axis by −θ. A sidebetween the points Sm1 and Sm2 is a segment that is orthogonal to theside between the points Sm4 and Sm1 and passes through a point Pb. Aside between the points Sm2 and Sm3 is a segment that is parallel to theside between the points Sm4 and Sm1 and passes through a point Pc. Aside between the points Sm3 and Sm4 is a segment that is parallel to theside between the points Sm1 and Sm2 and passes through a point Pd.

A scan direction (see an arrow with a solid line) of the ion beam in thescan pattern Sp11 is a direction directed from the point Sm4 toward thepoint Sm1.

A sweep direction of the ion beam in the scan pattern Sp11 is adirection that is perpendicular to the scan direction and that isdirected from the point Sm1 toward the point Sm2 or from the point Sm2toward the point Sm1.

A width of each scan line in the scan pattern Sp11 is identical to alength of the side between the points Sm4 and Sm1.

Although illustration of other scan patterns Sp12, Sp13, and Sp14 in themodification is omitted, the other scan patterns are obtained byreversal of the scan direction and symmetrical transformation withrespect to the y axis.

For example, the scan pattern Sp12 has the scan direction reversed inthe scan region SB1

For example, the scan pattern Sp13 is a scan pattern that is equivalentto reversing the scan pattern Sp11 to shown left and right (in anx-axial direction). The scan pattern Sp13 is obtained by symmetricaltransformation with respect to the y axis.

For example, the scan pattern Sp14 has a scan direction reverse to thescan direction of the scan pattern Sp13.

When the image acquiring region P is a square, and when θ=45°, the scanregion SB1 is a square that is a type of the rectangle. A scan regionSB2 is homologous to the scan region SB1. At this point, the scandirections of the scan patterns Sp11 and Sp13 are directions directedfrom the point Sm4 toward the point Sm1, and the scan directions of thescan patterns Sp12 and Sp14 are directions directed from the point Sm2toward the point Sm1.

According to this modification, except that the scan and the sweep areperformed using the scan patterns Sp11 to Sp14 in place of the scanpatterns Sp1 to Sp8, this modification is made identical to the firstembodiment, and can acquire an image of the image acquiring region P.

Hereinafter, the method for acquiring the image of this modificationwill be described centered on differences from the first embodiment.

Step S1 of this modification is the same step as step S1 of the firstembodiment.

In step S2 of this modification, the ion beam irradiation control device21 is adapted to control four types of scans and sweeps using the scanpatterns Sp11 to Sp14. At this point, an amount of irradiation of theion beam is set to D/4.

Here, D is an amount of irradiation of ions with which a good image canbe acquired by one scan and sweep of the range of the scan region SB1.

In this modification, the scan direction and the sweep direction of theion beam are orthogonal to each other. For this reason, control of thescan and the sweep in each scan pattern is nearly equal to scan andsweep operations when known raster rotation is performed in the ion beamapparatus.

In step S2 of this modification, as a result of the scan and the sweepin the four types of scan patterns, scan region image data Gs11 to Gs14corresponding to the scan patterns Sp11 to Sp14 are stored in thestorage 24.

Step S3 of this modification is different from that of the firstembodiment only in that the operation of detecting the amount ofposition offset, the operation of correcting the amount of positionoffset, and the operation of synthesizing the image are performed usingthe scan region image data Gs11 to Gs14.

That is, scan region image data gs11 to gs14 corrected on the basis ofthe amounts of position offset of the scan region image data Gs11 toGs14 are generated. The calculator 25 synthesizes the scan region imagedata gs11 to gs14 to generate image acquiring region image data GP ofthe image acquiring region P.

Step S4 of this modification is the same step as step S4 of the firstembodiment.

In this modification, a shape of the scan region is a square or arectangle of a parallelogram by way of example.

With regard to the inside of the image acquiring region P, the scanpatterns have only four types, and the scan directions of the edges 30 aof the metal line patterns 30 are four directions that are identical andoblique.

For this reason, the modification is made completely identical to thefirst embodiment, and can reduce a distance at which the ion beam passesthrough the insulating part when the ion beam passes through theisolated pattern 32.

As a result, when an image of the dielectric substrate in which theconducting parts having the linear edges are formed is acquired usingthe ion beam, an image in which the influence of electrification of thedielectric substrate is reduced can be easily acquired.

In the scan pattern of the first embodiment, the scan regions outsidethe image acquiring region P are formed only outside the two sides ofthe image acquiring region P.

In contrast, in this modification, since the scan direction and thesweep direction are orthogonal to each other, the scan regions outsidethe image acquiring region P are formed outside the respective sides ofthe image acquiring region P. A region in which the ion beam is scannedand swept with the same number of sweeps as the inside of the imageacquiring region P is generated at each side of the image acquiringregion P.

For example, as illustrated in FIG. 12, when the image acquiring regionP is a square, and when θ=45°, in this modification, a triangle havingthe points Sm1, Pa, and Pb outside the image acquiring region P as thevertexes, a triangle having the points Sm2, Pb, and Pc as the vertexes,a triangle having the points Sm3, Pc, and Pd as the vertexes, and atriangle having the points Sm4, Pd, and Pa as the vertexes are isoscelestriangles that are congruent to each other.

For this reason, regions of these triangles are subjected to four scansand sweeps of the ion beam in the same way as the inside of the imageacquiring region P.

Thus, the outside of the image acquiring region P suffers the sameirradiation damage as the inside of the image acquiring region P.

When it is determined that the irradiation damage to the outside of theimage acquiring region P is great, as in the first embodiment, it ispreferable to obliquely intersect the scan direction and the sweepdirection, and to use the parallelogrammic scan pattern in which thesweep direction is parallel to one side of the image acquiring region P.

Second Embodiment

An ion beam apparatus of a second embodiment of the present inventionwill be described.

FIG. 13 is a schematic system configuration view illustrating an exampleof a configuration of the ion beam apparatus of the second embodiment ofthe present invention.

The ion beam apparatus 40 of the present embodiment illustrated in FIG.13 is an apparatus for performing only both observation of a sample 44using an ion beam and a sputtering process caused by irradiation of theion beam. The sample 44 is not limited to the mask in the firstembodiment. However, a sample in which an insulating part and conductingparts are mixed is suitable, and the sputtering process caused by theirradiation of the ion beam refers to a process of forming a crosssection of the sample 44, or the like.

The ion beam apparatus 40 is provided with an ion beam column 41, adetector 48, and a control device 50 in place of the ion beam column 11,the detector 18, and the control device 20, and dispenses with theetching gas feeder 16 and the deposition gas feeder 17 of the ion beamapparatus 10 of the first embodiment.

Hereinafter, the second embodiment will be described centered ondifferences from the first embodiment.

The ion beam column 41 does not perform a repair operation.

The detector 48 detects secondary charged particles based on the ionbeam radiated to the sample 44 from the ion beam column 41.

As the secondary charged particles, the detector 48 detects, forinstance, secondary ions, secondary electrons, etc. generated from thesample 44.

In association with the removal of the etching gas feeder 16 and thedeposition gas feeder 17, the control device 50 is configured byremoving a function of controlling these feeders from the control device20 of the first embodiment.

For this reason, although detailed illustration is omitted, the controldevice 50 is provided with an ion beam irradiation control device 21, animage data generator 23, a storage 24, a calculator 25, and a displaycontrol device 26, which are the same as the first embodiment.

The control device 50 according to the present embodiment perform thesame operation as the control device 20 according to the firstembodiment except that the repair operation is not performed.

According to the ion beam apparatus 40 of the present embodiment, thesecond embodiment is made identical to the first embodiment, and animage of an image acquiring region P in a sample 44 can be acquired.

According to the ion beam apparatus 40 of the present embodiment, thesecond embodiment is made identical to the first embodiment, and stepsS1 to S4 can be performed.

For this reason, when the ion beam apparatus 40 is made identical tothat of the first embodiment, and when it acquires an image of adielectric substrate in which the conducting parts having the linearedges are formed using the ion beam, the ion beam apparatus 40 caneasily acquire an image in which the influence of electrification of thedielectric substrate is reduced.

Further, in the description of each of the embodiments and the firstmodification, the case in which the image of the image acquiring regionis acquired by radiating the plurality of ion beams in the scandirection or the sweep direction within the scan region by means of theplurality of scan patterns has been described by way of example. Thefour or eight types of scan patterns are exemplified, but the number ofscan patterns is not limited thereto.

The number of scan patterns may be one. For example, an image that isnot influenced by the charged electric charges may be acquired dependingon the type of the mask pattern of the mask 14 even when the pluralityof scan region image data in which the scan direction of the ion beam orthe scan region is changed are not acquired. In this case, it is notessential to acquire the plurality of scan region image data.

In this case, in the third operation, the image data of the imageacquiring region may be generated only by the calculation of extractingthe image data within the image acquiring region from one scan regionimage data.

In the description of the first modification, the case in which thetotal of four scans and sweeps are performed one by one by the scanpatterns Sp11 to Sp14 has been described by way of example. However, thescan region image data may be generated by performing a plurality ofscans and sweeps by means of the same scan pattern. In this case, thesame number of scans and sweeps is performed on each scan pattern, whichis preferable in obtaining a good image.

For example, in the first modification, the image acquiring region imagedata may be generated by performing the two scans and sweeps on the scanpatterns Sp11 to Sp14 and performing image processing on the basis ofthe total of eight scan region image data. However, in this case, theamount of irradiation of the ion beam in the one scan and sweep is setto be D/8.

In the description of each of the embodiments and the firstmodification, the case in which the shape of the scan region of the scanpattern abuts the sides or the apexes of the image acquiring region hasbeen described by way of example. However, the shape of the scan regionmay be a shape within which the image acquiring region is includedwithout abutting the image acquiring region.

In the description of each of the embodiments and the firstmodification, the case in which, before the operation of synthesizingthe image (the third operation) is performed, the operation of detectingthe amount of position offset (the fifth operation) and the operation ofcorrecting the amount of position offset (the sixth operation) areperformed has been described by way of example. However, when it isknown that the amount d of whole position offset of the image data issmall, for instance, when the mask 14 is hardly charged, the fifthoperation and the sixth operation may be omitted.

In this case, the scan region image data synthesized by the thirdoperation is based on the scan region image data itself generated by thesecond operation.

Although the preferred embodiments of the present invention have beendisclosed, the present invention is not limited to these embodiments andtheir modifications. Additions, omissions, and substitutions of theconfiguration and modifications thereof are possible without departingfrom the scope and spirit of the invention.

Further, the present invention is not limited by the above description,and is defined by the accompanying claims.

What is claimed is:
 1. A method for acquiring an image, in which animage of an image acquiring region is acquired by radiating an ion beamto a sample having a conducting part with a linear edge on a dielectricsubstrate, the method including: a first operation of performing anequal-width scan by the ion beam in a first direction that obliquelyintersects the edge and sweep in a second direction intersecting thefirst direction, and radiating the ion beam to a scan region of aparallelogram shape which is wider than and which includes the imageacquiring region; a second operation of detecting secondary chargedparticles generated by radiating the ion beam and generating an imagedata of the scan region; a third operation of calculating the image dataof the scan region and thereby generating an image data of the imageacquiring region; and a fourth operation of displaying the image data ofthe image acquiring region, wherein the first operation is performed aplurality of times to different scan regions of the parallelogram shapeeach of which includes the image acquiring region by changing at leastone of a scan direction of the equal-width scan and a sweep direction ofthe sweep and setting the output of the ion beam such that a totalamount of irradiation of the ion beam in the image acquiring regionbecomes an amount of irradiation required when an image is acquired byone sweep; the second operation is performed after the first operationis performed each of the plurality of times; and the third operationgenerates the image data of the image acquiring region by synthesizing aplurality of image data based on the image data of a plurality of thescan regions generated by the second operation performed a plurality oftimes.
 2. The method according to claim 1, further including: beforesynthesizing the image data on the basis of the image data of aplurality of the scan regions in the third operation, a fifth operationof detecting an amount of position offset between the image data in thescan region that is generated by the second operation performed at leastfor the first time, and the image data in the scan region which isgenerated by the second operation performed for the final time, amongthe second operations which performed the plurality of times; and asixth operation of correcting the amount of position offset of the imagedata in the plurality of the scan regions on the basis of the amount ofposition offset detected by the fifth operation.
 3. An ion beamapparatus including: an ion beam column configured to generate an ionbeam to acquire an image of an image acquiring region of a dielectricsubstrate on which a conducting part with a linear edge is formed andradiate the ion beam to the dielectric substrate; a movable stageconfigured to support the dielectric substrate to be movable within atleast a plane intersecting an optical axis of the ion beam column; anion beam irradiation control device configured to control the ion beamcolumn to perform equal-width scan by the ion beam in a first directionthat obliquely intersects the edge and sweep in a second directionintersecting the first direction and thereby radiate the ion beam to ascan region of a parallelogram shape wider than the image acquiringregion; a detector configured to detect secondary charged particlesgenerated from the dielectric substrate when the ion beam is radiated;an image data generator configured to generate image data of the scanregion on the basis of the detection output of the detector; a storageconfigured to store the image data of the scan region; a calculatorconfigured to calculate the image data of the scan region to generateimage data of the image acquiring region; and a display unit configuredto display the image data of the image acquiring region, wherein the ionbeam irradiation control device causes the ion beam column to radiatethe ion beam a plurality of times to different scan regions of theparallelogram shape each of which includes the image acquiring region bychanging at least one of a scan direction of the equal-width scan and asweep direction of the sweep and setting the output of the ion beam suchthat a total amount of irradiation of the ion beam on the imageacquiring region becomes an amount of irradiation required when an imageis acquired by one sweep; and the calculator generates the image data ofthe image acquiring region by synthesizing the image data based on theimage data of a plurality of the scan regions generated by the imagedata generator when the ion beam is irradiated a plurality of times. 4.The ion beam apparatus according to claim 3, wherein the calculator isconfigured to: detect an amount of position offset between the imagedata in the scan region which is generated at least for the first timeamong the image data in the plurality of the scan regions and the imagedata in the scan region which is generated for the final time; andcorrect the amount of position offset of the image data in the pluralityof the scan regions on the basis of the detected amount of positionoffset.